Exhaust gas after treatment systems are commonly used in conjunction with diesel engines for reducing the amount of nitrous oxides (NOx) in an exhaust gas. One type of after treatment system includes an injector for spraying a reduction agent, such as ammonia, fuel or urea, into the exhaust gas. The exhaust gas is then transported to a mechanism such as a catalytic converter, where the amount of nitrous oxides in the exhaust gas is reduced as the reduction agent reacts with the nitrous oxides in the exhaust gas to form water and nitrogen. After reacting in the catalytic converter, the exhaust gas is released from the catalytic converter and ultimately to the atmosphere.
In one type of after treatment system, the injector may include at least one orifice, such as an injection orifice, for spraying the reduction agent into the exhaust gas. The injector may spray a mist of the reduction agent into the exhaust gas. A very fine mist of reduction agent is typically desirable. Spraying droplets of reduction agent that are smaller in size usually results in a more efficient reaction between the reduction agent and the exhaust gas. As the pressure drop across the injector orifice increases, the size of the droplets of the reduction agent generally decreases, and the injector sprays a finer mist of the reduction agent into the exhaust gas.